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通过蠕变性能测试和组织形貌观察,研究了铸态TiAl-Nb合金在近890~910℃温度区间的蠕变行为。结果表明,铸态TiAl-Nb合金的组织结构主要由层片状γ/α_2两相组成,不同取向γ/α_2两相层片状组织之间存在不规则锯齿状形态的晶界,该锯齿状非层片晶界由单一γ相组成。在高温蠕变期间,合金具有较好的蠕变抗力和较长的蠕变寿命;合金在蠕变期间的变形机制是大量位错以位错列的形式剪切层片状γ/α_2两相,其中,大量位错在基体中滑移,发生反应可形成位错网,可促进位错的攀移,减缓应力集中,改善合金的蠕变抗力。与α_2-Τi_3Al相比,γ-TiAl相有较弱的强度。因此,蠕变期间合金中的裂纹易于在与应力轴呈45°角、且与层状结构相平行的晶界处萌生与扩展,直至蠕变断裂是合金在蠕变期间的断裂机制;其中,与层状结构相平行的断口呈光滑表面,而与层状结构呈一定角度的断裂表面存在撕裂棱,为较高强度的α_2-Ti_3Al相阻碍裂纹扩展所致。
The creep behavior of as-cast TiAl-Nb alloy in the temperature range of 890 ~ 910 ℃ was studied by creep test and microstructure observation. The results show that the microstructures of the as-cast TiAl-Nb alloy consist mainly of lamellar γ / α 2 phases, and there are irregular jagged grain boundaries between the lamellar structures of γ / α 2 lamellae with different orientation. The non-lamellar grain boundaries consist of a single gamma phase. During high temperature creep, the alloy has better creep resistance and longer creep life. The deformation mechanism of the alloy during creep is that a large amount of dislocations shear the lamellar γ / α_2 two phases in the form of dislocation arrays Among them, a large number of dislocations slide in the matrix, the reaction can form a dislocation network, can promote the displacement of dislocations, reduce stress concentration and improve the creep resistance of the alloy. Compared with α_2-Τi_3Al, γ-TiAl phase has weaker strength. Thus, cracks in the alloy during creep tend to germinate and expand at grain boundaries that are 45 [deg.] To the stress axis and parallel to the lamellar structure until creep rupture is a fracture mechanism of the alloy during creep; The fracture parallel to the layered structure has a smooth surface, while the fracture surface at a certain angle with the layered structure has a tear edge, which hinders the crack growth due to the higher strength α_2-Ti_3Al phase.